The present invention relates generally to the field of methods and medical devices for cardiac pacing and for modulating cardiac muscle activity and contractility and more specifically to the field of methods for determining timing of delivery of excitable tissue controller (ETC) signals under a variety of conditions including varying heart rates, paced or sensed triggering and the absence and presence of ETC signals.
Excitable tissue controllers (ETCs) are devices which modulate the activity of excitable tissues by application of non-excitatory electrical stimulation to the excitable tissue through suitable electrodes in contact with the tissue. For example, ETC devices may be used, inter alia, to increase or decrease the contractility of cardiac muscle in vitro, in vivo and in situ., as disclosed in detail in PCT application, International Publication Number WO 97/25098 to Ben-Haim et al., titled xe2x80x9cELECTRICAL MUSCLE CONTROLLERxe2x80x9d, incorporated herein by reference. Other methods and applications of ETC devices are disclosed in PCT applications commonly-assigned to the assignee of the present application, International Publication Number WO 98/10828, titled xe2x80x9cAPPARATUS AND METHOD FOR CONTROLLING THE CONTRACTILITY OF MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference, International Publication Number WO 98/10829, titled xe2x80x9cDRUG-DEVICE COMBINATION FOR CONTROLLING THE CONTRACTILITY OF MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference and International Publication Number WO 98/10830, titled xe2x80x9cFENCING OF CARDIAC MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference, International Publications Number WO 98/10831 to Ben Haim et al., titled xe2x80x9cCARDIAC OUTPUT CONTROLLERxe2x80x9d, incorporated herein by reference.
Further applications of the ETC including devices combining cardiac pacing and cardiac contractility modulation are disclosed in PCT Application, International Publication No. WO 98/10832, titled xe2x80x9cCARDIAC OUTPUT ENHANCED PACEMAKERxe2x80x9d so Ben Haim et al., co-assigned to the assignee of the present application. Such ETC devices function by applying non-excitatory electrical field signals of suitable amplitude and waveform, appropriately timed with respect to the heart""s intrinsic electrical activity to selected cardiac segments. The contraction of the selected segments can be modulated to increase or decrease the stroke volume of the heart. The timing of the ETC signals must be carefully controlled since application of the ETC signal to the myocardium at inappropriate times may be arrhythmogenic. The ETC signals must therefore be applied to the selected cardiac segment within a defined time interval during which the selected cardiac segment will not be stimulated by the ETC signals.
As disclosed in International Publication No. WO 98/10832, the ETC signals may be timed relative to a trigger signal which is also used as a pacing trigger, or may be timed relative to locally sensed electrogram signals.
U.S. Patent Application to Mika et al., Ser. No. 09/276,460, Titled xe2x80x9cAPPARATUS AND METHOD FOR TIMING THE DELIVERY OF NON-EXCITATORY ETC SIGNALS TO A HEARTxe2x80x9d, filed Mar. 25, 1999 and assigned to the common assignee of the present application, the entire specification of which is incorporated herein by reference, discloses a method for timing the delivery of non-excitatory ETC signals to a heart using, inter alia, an alert window period for reducing the probability of delivering an improperly timed ETC signal to the heart due to spurious detection of noise or ectopic beats.
The methods of timing of the delivery of ETC signals disclosed hereinabove do not take into account the fact that naturally occurring and pacemaker induced changes in heart rate (HR) may cause changes in the velocity of propagation of the depolarization wave in the myocardium. Additionally, the delivery of the ETC signals to the myocardium may also cause changes in the velocity of propagation of the depolarization wave in the myocardium. Other factors such as, inter alia, various cardio-active drug treatments and myocardial pathological conditions such as ischemia may also cause changes in the velocity of propagation of the depolarization wave in the myocardium. It is therefore desirable to have a method for determining proper timing of the delivery of ETC signals which takes into account variations in velocity of propagation of the depolarization wave in the myocardium under different cardiac conditions.
Accordingly, it is an object of the present invention to provide apparatus and methods for obtaining data from a heart of a patient. The obtained data is useful for on-line determining of the parameters of a detection time window. The detection time window is used in an ETC device to detect depolarization events for triggering the application of non-excitatory ETC signals to the heart of the patient. The detection time window is also referred to as the xe2x80x9calert time windowxe2x80x9d or xe2x80x9calert windowxe2x80x9d hereinafter.
A feature of the present invention is the applying of electrodes to a first cardiac site and a second cardiac site of the patient. The electrodes are operatively connected to a data collection device. In accordance with one preferred embodiment of the present invention the first cardiac site is in or about the right ventricle of the heart and the second cardiac site is in or about the left ventricle of the heart. In accordance with another preferred embodiment of the present invention the first cardiac site is in or about the right atrium of the heart and the second cardiac site is in or about the left ventricle of the heart.
In accordance with a preferred embodiment of the present invention, the device has circuitry adapted for sensing and detecting cardiac depolarization events using one or more of the applied electrodes and for delivering non-excitatory ETC signals to the heart. In accordance with another preferred embodiment of the present invention, the device may also include circuitry for delivering pacing pulses to one or more sites of the patients heart.
Another feature of the present invention is the triggering of a data collection time interval for detecting depolarization events at the second cardiac site. In accordance with one preferred embodiment of the present invention, the data collection time interval is triggered by the detection of a depolarization event at the first cardiac site. In accordance with another preferred embodiment of the present invention, in a device capable of delivering pacing pulses to the heart, the data collection time interval is triggered by the detection of a depolarization event at the first cardiac site or by the delivery of a pacing pulse to the first cardiac site.
The data collection time interval is virtually divided into a plurality of contiguous time bins. All of the time bins have an identical duration which is smaller than the duration of the data collection time interval.
The data collection device includes a memory for storing a plurality of histogram data sets. Each of the histogram data sets is stored in the memory of the device as a separate data structure including a plurality of data elements. Each of the data elements of a histogram data set is associated with a single time bin of the data collection interval. The number of time bins is identical to the number of data elements included in any of the data histogram sets. The value stored in each of the data elements is an integer number representing the cumulative number of depolarization events detected within the time bin associated with the data element at said second cardiac site in a plurality of cardiac beats.
Each of the plurality of the histogram data sets represents a cumulative time distribution histogram of cardiac depolarization events detected at said second cardiac site in a plurality of cardiac beats.
Each histogram data set is associated with a plurality of histogram parameters. The histogram parameters have values indicative of the cardiac conditions common to the plurality of cardiac beats used to obtain the histogram data set. The histogram parameters include a sensitivity level parameter having a value indicative of the detection sensitivity level used for detecting the cardiac depolarization events of the plurality of cardiac beats used for acquiring the data of the histogram.
Typically, the data is acquired by recording data from a plurality of cardiac beats under a variety of different cardiac conditions. The beat""s cardiac conditions may include beats induced by natural pacing of an intrinsic cardiac pacemaker such as the heart""s sino-atrial node (referred to as sensed beats), beats induced by delivering an artificial pacing pulse to the heart (referred to as paced beats), beats for which prior application of ETC signals to the heart has induced a substantial change in the velocity of propagation of a depolarization wave in a part of the myocardium and beats for which prior application of ETC signals to the heart has not induced a substantial change in the velocity of propagation of a depolarization wave in a part of the myocardium. The cardiac conditions also include the cycle length of the beats which is the beat to beat time interval as obtained from the measured R-R interval or A-A interval depending on the choice of the first cardiac site. All the beats used for obtaining a specific histogram data set have a beat cycle length which is within a certain range of cycle lengths associated with that specific histogram data set. Each of the histogram data sets is also associated with a particular detection sensitivity level which was used for detecting of the depolarization events at the second cardiac site during the data collection time interval of each of the beats which are sampled for the histogram data set.
The histogram data sets may be collected in the patient during a data acquisition period in which the patient may perform a regime which includes certain physical exercise types top ensure that a sufficient number of beats are sampled for a suitable range of heart rates. If the data collecting device includes pacing capabilities, the A-V delay of the pacing circuitry may be varied manually or automatically to ensure a desired ratio of paced to sensed beats.
After the histogram data sets are acquired, they may be telemetrically or non-telemetrically transferred to an analyzing unit for processing. The analyzing unit may be a separate device external to the patient or may be part of a data collection device which is disposed outside of the patient. The histogram data sets are processed to provide a plurality of sets of alert window parameters which are found to yield a desired level of event detection. The plurality of sets of alert window parameters may be programmed as an array or look up table (LUT) into an ETC device or pacemaker/ETC device such as the data collection device which is already implanted within the patient. If the data collection device is an external device disposed outside the patient, the array or LUT may be programmed into an ETC device or pacemaker/ETC device after they are connected to the electrodes and implanted in the patient. Each of the plurality of sets of alert window parameters may include a starting bin number and an ending bin number (in which case the array or LUT also includes the value of the bin duration for enabling on-line computation of the beginning and ending time points of the alert window) which are associated with a particular unique combination of cardiac condition parameters. Alternatively, each of the plurality of sets of alert window parameters may include a starting time and an ending time for the alert window which are associated with a particular unique combination of cardiac condition parameters.
The plurality of sets of alert window parameters may be further processed to derive a set of approximation parameters which may be used for computing of approximated alert window parameters which are corrected to account for the actual measured beat cycle length. The set of approximation parameters may be programmed as an array or look up table (LUT) into the ETC device or the pacemaker/ETC device. The approximation parameters may be computed using piece-wise linear approximation methods or other suitable approximation methods.
In accordance with a preferred embodiment of the present invention, the alert window parameter sets may also be in a partially degenerate form in that some or all of the parameters may have a single value for all the cardiac conditions. For example, if no pacing is performed by the data collection device, the values of the condition parameters associated with all the sets of approximation parameters are degenerate since they only have a value indicative of the beats being sensed beats and may not assume the value indicative of paced beats.
Another feature of the present invention is that the array or LUT which is obtained by processing the histogram data sets may also include a plurality of sets of detection sensitivity level parameters. Each set of detection sensitivity level parameters may include one or more parameters for on-line determination of the detection sensitivity level based on the current cardiac conditions. The number and type of the detection sensitivity level parameters depends on the detection method that was used in collecting the histogram data sets. For example, in accordance with one preferred embodiment of the present invention, event detection is performed by using a single positive threshold crossing criterion. In such a case, each set of detection sensitivity level parameters includes a single threshold value associated with a specific set of cardiac condition parameters. This single threshold value represents the threshold level to be used by the ETC device or pacemaker/ETC device of the patient under the cardiac conditions. Other event detection methods may also be used such as, but not limited to, morphological detection methods or combined slope and threshold methods. If such other detection methods are used, each set of detection sensitivity level parameters may include one or more detection sensitivity level parameters, depending on the particular event detection method used.
In accordance with other preferred embodiments of the present invention, the plurality of sets of detection sensitivity level parameters may also be a degenerate set. For example if the operator or user determines that a single detection sensitivity level may be used under all possible combinations of cardiac conditions, the detection sensitivity level parameters in all the sets of detection sensitivity level parameters in the array or LUT may have identical values.